The invention refers to a switch element with a push button for axial displacement of a contact carrier provided with contacts, which is contained in a housing, and charged or maintained by a return spring in zero position, and which is further equipped with notches or catches for receiving lock-in elements urged into the notches by lock springs.
The switch element according to German Patent DE-OS No. 2056 943 is a terminal or boundary switch, and has only one on- and off-position, and no other switch positions, as required for shifting different speeds of motors. The contact carrier or portion of this switch element protrudes with one actuator end, from the housing, and may there be operated directly by a machine part, but not however, by a finger or thumb, since it jumps abruptly into another position when exceeding dead center. When pressing down, it suddenly gives, which might be tolerable. However, when releasing or returning it has a sudden acceleration, which would manifest itself as a blow on the finger or the thumb.
Another single-stage terminal switch with spring-loaded push button in a series spring circuit is disclosed in German Patent DE-AS No. 1190 088. The positions of the spring circuit are maintained by permanent magnets. The spring circuit operates the electric terminal switch whose contacts are spring-loaded for fast spark-over. This arrangement is very involved and is also suitable for two switch positions only, not for stepped changes in speed.
It is therefore the object of this invention to provide an easily operable stepped switch element with a spring circuit for several switch positions. The push button is at rest or in off position via an initial stress spring mounted on the contact carrier or body for the switch. The carrier has notches provided in succession for several switch positions in the direction of movement of the contact carrier. The operator depresses the push button with his thumb, and thereby cocks the initial stress spring. Upon exceeding a predetermined pressure the contact carrier jumps to the next switch position, whereby the initial stress spring is released and the return spring is cocked. Although this changes the counter-pressure of the push button on the thumb, it does not disappear suddenly which would have an unpleasant effect. With further increase in pressure the initial stress spring is again cocked, and the lock springs are compressed, which upon passing the notch, drive the contact carrier into the next switch position and thereby further tense the return spring, while the initial stress spring is again released.
To shift back a motor controlled by the switch of the invention, the pressure on the push botton is reduced and the initial stress spring relaxes, while the contact carrier at first still remains in its position and the return spring is fully cocked. Only when the initial stress spring is almost relaxed the return spring force prevails over it, driving the contact carrier abruptly into the next notch, whereby the initial stress spring is again cocked. This is not felt as unpleasant by the thumb resting on the push button.
The notches are of varying depths. The notch for the rest position is the deepest and the most difficult to pass. Therefore, any slight and unintentional touch of the push button does not lead to the start-up of the motor. The notch for the second stage, i.e. for the overdrive, is the most shallow and can be left quickly for the first stage when relaxing the pressure on the push button.
As a further feature of the invention, the contact carrier is equipped with contacts of one switch position which are displaceable relative to the contacts of the other switch position. When actuating the push botton, all contact pairs, with the exception of one, are moved to reach the first switch position. However, only two contact pairs reach the respective contact junctions, while the other contact pair requires further movement of the push button and the contact carrier before it reaches the second switch position, at which time all contacts are closed for the supply of current.
Each contact pair is supported on each other by contact springs and guided in contact slots in the contact carrier in the direction of motion of the latter. In their terminal positions, the contacts adhere to contact junctions firmly attached in the switch element. Between contacts and contact stops of the contact carrier limiting the movement of the contacts in the latter, an initial stress distance is found. This initial stress distance facilitates partial relaxation of the contact spring when displacing the contact carrier in release or off direction of the respective closed contact. This relaxation is necessary, since during shifting of the contact carrier from one position to another the contacts must be removed suddenly from the contact junctions. A cocked contact spring would prevent this or at least make it more difficult. The initial stress distance is greater than half the distance between the rest cams forming the notches. The moment of the switch-over is thus always determined by the lock-in elements when jumping from one notch to another, and not by the springs whose strength can never be exactly determined, and whose force rations do not change abruptly.
As a further feature of the invention, the force of the return spring, several of which may be arranged side by side acting in conjunction upon the contact carrier, as well as the force of all contact springs and the force of the lock spring affecting the switch cam and checking its movement, in relaxed condition is weaker than the force of the initial stress spring when the latter is cocked. Upon passing the switch point, the contact springs are relaxed and the return springs are cocked. The contact springs will tense themselves again, while the return springs always remain cocked during the on-position. Their relaxation is prevented by the lock springs and the terminal pressure of the initial stress spring reduced by the switch path of the contact carrier. The initial stress spring is, at low tension, under such minor initial stress that, despite the support by the lock springs, it is weaker than the force of the return springs, which temporarily also tense the two opposite lock springs.
Preferably, pressure bases or extensions extend between the push button and the contact carrier for limiting the engagement of these parts. They maintain the functioning of the contacts of the first switch stage of the switch element even during breakage or fatigue of the initial stress spring, and forcibly effect the motion of the contact carrier. The pressure bases are arranged on the push button and guided in grooves of a push button borehole of the switch body cover plate. The latter has restrictive stops for the pressure bases or extensions, so that the push button cannot be pushed out of the switch body by the initial stress spring. The restrictive stops keep the initial stress spring adhering to the push button under a low initial stress at all times. Also, the contact carrier is arranged in a base body of the switch element. Its cover plate, which is screwed on, houses the push button in a borehole. This division makes assembly of the switch element with its mountings easy. The contact junctions and the contact carrier are inserted into the standing base, and the initial stress spring with push button are placed on the contact carrier. The cover plate is placed with the borehole over the push button and screwed to the base. The cover plate also keeps the U-shaped guides for the lock-in elements in the base body so as to keep the lock-in elements pressed into the notches on the contact carrier by the lock springs. Each U-shaped piece is provided at the inside of the flanges with guiding grooves for pegs or pins of the lock-in element as well as for a thrust bearing, between the lock-in element and the lock spring. At the end opposite the lock-in element, the U-shaped piece further has a peg for the lock spring. The contact junctions are inserted into grooves in the base of the switch.
An example of the invention is shown on the drawings and explained as follows.